This invention relates generally to hand tools. More particularly, the present invention relates to a composite hand tool having interchangeable and replaceable striking heads, and a related assembly process.
Traditionally, in percussive tools such as sledge hammers, the tool head includes an aperture or eyehole through its body which has a single or double taper. In both cases, the taper expands at the top of the tool head or that portion which is normally directed away from the user when the tool is in use. When a wooden handle is driven through the eyehole from the bottom side of the tool head, the excess wood protruding from the top side is cut off, and some wedging device, such as an ordinary wedge, is driven into the wood so that the upper end thereof is expanded to provide an inverted frustum which, theoretically, is tightly expanded into the tool eyehole. The expanded section of wood must fit within the upper tapered portion of the eyehole tightly so that the head cannot fly off during use. This is a very elemental assembly which has been in use for many years.
Recent years have seen the development of extremely strong composite tool handles formed of reinforcing fibers cured within a resin composite. Such reinforcing fibers may include fiberglass, polyester, boron, kevlar or graphite, and suitable resin composites include polyester, epoxy, phenolics, etc. With the development of these composite materials, the shaft underneath the tool head can now be made with a cross-section small enough to pass through the conventional eyehole of percussive tool heads, and yet be strong enough to withstand the impact forces likely to be encountered.
As advanced materials have been introduced to replace wood, the materials have been either bonded into the eyehole of the tool, substituting the bond for the old traditional wedge, and/or welded such as metal to metal. Whereas these techniques are suitable to some degree for the manufacture of original tools in which the handle is installed with appropriate machinery and equipment at a factory, the techniques are not suitable when practiced in the field. In the case of bonding, composite shafts have been attached to tool heads primarily by means of adhesives in the epoxy field. When utilizing such adhesives, despite the continued development of these materials, it takes care, precision and good workmanship to properly install a replacement handle in a tool head reliably in the field with no secondary tools to assist. Even in factories where the tool head is installed on a production basis, high levels of quality control must be practiced in order to insure that the head is secured to the handle under all anticipated working conditions. Further, since the high strength composite shafts are usually inadequate in cross-sectional size to be comfortable for a user's hands, a grip of rubber or some other plastic material is usually molded onto the shaft or subsequently bonded thereto in a manner which guarantees that the grip will not accidentally slide off the shaft.
U.S. Pat. No. 5,056,381 illustrates a hand tool which addresses many of the drawbacks of the prior art discussed above. There a replacement tool handle for a percussive tool is shown which includes a high strength, load-bearing rod which is inserted through the eyehole of a tool head from its upper end, a grip which ensheathes a portion of the rod projecting from a lower end of the tool head, and two interlocking members which fasten the grip to the rod. The rod includes a handle shaft capable of passing completely through the eyehole of the tool head, and a shaft retainer located at a first end of the shaft for preventing an adjacent end of the rod from passing through the eyehole. The shaft retainer forms a generally frusto-conical slug having an outer surface portion generally corresponding to a portion of the eyehole, an enlarged portion which is incapable of passing through the eyehole, and an inner cavity in which the first end of the shaft is secured. Both the handle shaft and an internal cavity provided the grip have non-circular cross-sections to prevent turning of the grip relative to the shaft. The interlocking members each include tooth portions which engage one another within the outer periphery of the handle in a manner which denies access to a user, thus ensuring a permanent connection.
With the trend toward miniaturization in many industries, there has developed the need for specialized tools to service new lines of product. This applies to striking tools (with percussive tool heads) as well as other specialty tool products. For example, maintenance people who service computers, copy machines, typewriters and the like must be able to carry a variety of striking tools in a very compact space.
Accordingly, there is a need for a novel hand tool which has interchangeable and replaceable striking heads, wherein a single handle may be packaged with a number of different types of striking heads into a kit which is compact and easily utilized in the field by maintenance people. The hand tool must be of such a construction that the tool head and the tool handle may be assembled to one another reliably and efficiently in such a manner which effectively prohibits the tool head from flying off the handle unintentionally. Preferably, the assembly should include a minimum number of separate parts, and should utilize standard manufacturing processes in order to reduce overall costs. Moreover, such a hand tool should permit use of a wide variety of striking tips having differing characteristics in order to maximize the flexibility of the resultant product. The present invention fulfills these needs and provides other related advantages.